Greenhouse gas emissions from agriculture and land use change

The carbon dioxide that plays a role in anthropogenic global warming is either from sediments including fossil fuels and cement production, or from soils and biomass. This relates to the well known carbon cycle. The carbon in soils and biomass can be transferred to the atmosphere via phenomena like fire and drought, while fossil fuels in the ground generally stay there (except for human activity and some volcanos). A planet with more carbon in soils and biomass and less in sediments is therefore for better or for worse different to a planet with more carbon in sediments and less in soils and biomass.

This suggests that the externality of greenhouse pollution from burning fossil fuels is qualitatively slightly different to the externality of greenhouse pollution from land clearing. Another issue is there is often much more uncertainty with measuring emissions from land clearing and deforestation, or CO2 sequestered by planting trees or reducing overgrazing. Other greenhouse gases also play a role – there are also issues with uncertainty when estimating methane emissions from cattle.

Reforestation and avoided deforestation can have huge cobenefits in terms of reducing habitat destruction which is an important driver of extinction. Unfortunately it is harder to measure emissions from activities with strong cobenefits such as biodiversity plantings or avoided deforestation than it is measure emissions from activities with less cobenefits, such as monoculture tree plantations.

Hansen’s recent paper suggests that when albedo and carbon cycle feedbacks are taken into account then climate sensitivity rises to around 6 degrees for a doubling of CO2. Hansen then suggests that “If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm. … An initial 350 ppm CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting agricultural and forestry practices that sequester carbon.” It is therefore important that we address both parts of the carbon cycle.

In an emissions trading market credibility is vital, uncertainty in measurement could undermine that. In a submission to the Garnaut review, I argued that some money raised from auctioning permits could be spent on activities such as biodiversity plantings until land use could be included. But perhaps these issues with uncertainty will always be significant. Maybe we need to create a parallel market in emissions related to agriculture and forestry. This could either be price based or quantity based. Perhaps uncertainty issues would mean a price (tax) based approach would be better, with activities that sequester carbon having a negative tax.

While it is relatively easy to measure the carbon sequestered from something like a monoculture tree plantation, it is more difficult to measure the carbon sequestered from restoring an ecosystem, or at least to have the carbon sequestered accredited. Reforestation and avoided deforestation can have huge cobenefits in terms of reducing habitat destruction which is an important driver of extinction. We need to learn as fast as possible how much carbon is sequestered through activities such biodiversity plantings and reducing grazing from cattle.

There is also the issue of emissions from logging and burning old growth native forests. At present only land that is converted from a ‘kyoto forest’ to land which is not a ‘kyoto forest’ or vice versa is included, so if you log an old growth forest, which stores huge amounts of carbon in both its soil and biomass, and then burn it, then because a forest will grow back, the emissions from logging and burning are not included in our greenhouse gas accounts. We need to learn as quickly as possible how to measure the GHG emissions from all kinds of emissions, including forest degradation and grazeland degradation.

Forest degradation and rangeland degradation do not get mentioned in the Green Paper, but it does suggest that carbon sequestered in forest products should be included in an international climate change framework. This is a similar approach to Australia’s reporting to the UNFCCC (which is slightly different to Kyoto accounting), where carbon sequestered in wood products is reported but emissions from forest degradation and rangeland degradation appears not to be. The could be construed as a way that Australia is gaming international climate negotiations. Or it could be a result of the government being influenced by rent seeking from native forest logging industries. Ironically, if forest degradation and rangeland degradation were included, it would probably be much easier for Australia to reduce its emissions.

We also need to learn as quickly as possible how much emissions are sequestered through sustainable land use practices that sequester carbon. We should also consider the possibility that there will always be significant uncertainties about how much will be sequestered. The best way to learn is by doing, so the question becomes how do we fund a whole lot of different environmentally appropriate activities that sequester carbon that we can learn from?

2 Responses to “Greenhouse gas emissions from agriculture and land use change”

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